BergvesenetPostboks 3021, 7002 Trondhcim Rapportarkivet

Bergvesenet rapport nr

BV 1845

Kommer fra ..arkiv

Rapport lokalisering Gradering

Trondheim

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Intern Journal nr Internt arkiv nr

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Fagområde

Geologi

Forekomster

Løkken

Dokument type

EmneordRåstofftype

Malm/metall

Sarnmendrag

Tittel

A report on some aspects of the geology of the Løkken Area

Forfatter

Dato 'Bedrift

Rutter, E. H.

Sept.1968

Kommune Fylke Bergdistrikt 150 000 kartblad 1250 000 kartblad

Meldal Sør-Trøndelag Trondheimske

111

•

A REPORT

ON

.SO:SAS:ECTS OF THE GEOLOGY

OF THE LØKKEN ARSA

by

E. H. Rutter

September 1968

1

INTRODUCTIDN

This is an interim report on the geologicn1

mapning of the Løkken Area. It is intended to

supplementwhat has been said in earlier reports

by myself and my colleagues and the general description

of the geology of this area submittedas a paper

to NGU in December 1967.

• Most of the fieldwork this summer has concentrated

on more detailed observation of the stratigraphyand

structure of the schistose rocks forming the northern

flank of the Løkken Synform and the complementary

folds to the north.

•

?he convontionni arosent a_

1 hfor= on as in the for:r of a ;720i0t0a:

a atze=ts zo s thesise field observ-- ons and

ho nazhors inzerpra on those observazions. T

anuu acc=anied arizten exelanation of

releyant details where necessarj.

hesis of the arca cov2reo ba four of

the new I :13 , 033 z000graohic taas is eresenzed with

this reaort. 7nese shects bear nea riv all of the structural

dnza colleoted in thoso nrcas. In addit lon, all of the

structurn1 data is oresented in the forzz of data sheets

harzoo-co rafefehces o the fiold exaosares where c

raeasurc dorts wore riade. The field exaosures are located

b, nuzzbers oh tho 1 :15,000 air r,hotO overlays which

usod for ua urnoscs. Tithoiogies, too are

indicatad on the overLays. Ir. Cha-= hcs arrangej h's

dcta th c sirnilar fashich, and this teo is inctueed 7:ith

r‘?"-) Or:.

It is ho-ad that this r:ethod of oresentao on will

- rove osz convenient for any further analysls which

be dasi and wilT facilizate the evehtual coezoi

of a c atiate JTeoloicul anaiysis od tUis re.:5. 1oh, when the

Sausic Voicies in tar: ic-ciar, have heer t ore

thorou

structure of the area,

as ftr as is .rnown az oresent, is interpreted with the

helo of o cross section.

3

NUMBERING OF THE OVERLAYS AND DATA SHEETS

The exposureswhere orientationreadings were

made are listed sequentiallyin the data sheets. Where

there are gaps in the numer&cal sequence,these refer

to 4osures where rock type observationsonly were made

and where no readingswere taken. These exposures are

sometimesnumbered on the air photo overlays, however.

Note : The terms used to describe fold geometry In

this report are, unless otherwise stated, those

suggestedby Fleuty ( Proc. Geol. Assoc., 1964 ).

Explanation of $ mbols used on the Geolo,ic..1Ma s.

.30/i nOrientationof f1 SchistositySurfaces .

Orientationof Surfaces of Primary Layering.

Orientationof f2 SchistositySurfaces.3o/iyo (CrenalationCleavage)

Plunge of Principal.fl Elongation,i.e. Direction of longest axis of deformed

304" objects such as pillows, vesicles, pebblesand spherulites,without reference to anypossible original shape anisotropy.

Plunge of f2 lineation,usually a crenulationlineation oni.thesurface of f1 schistosity,or axial direction of f2 minor folds.\3°MoFold axial direction,given by axialF ldirection of f1 minor folds or by

3 0/95bedding/cleavageintersection.

Fault - observed

Fault - inferred

-7-1N 1r- Low angle fault (thrust) - observed

11 11 11 11 11 inferred

7dthological Boundary - Observed

inferred

Horizontal Component of Younging Direction :

Right way up )Primary

{FeaturesInvertedonly

Bedding Cleavage IntersectionIndicatedby the"equivalentminor fold",but bearing the letter "c" instead of "f",with a subscript indicatingthe phase ofdeformation.Thearrow indicated the directionwhich gives the recorded sense of asymmetry.

Minor Fold Asymmetry -Indicatedby a minor fold symbol withthe letter "f", bearing a subscrintwhichindicatesthe nhase of deformation,andan arrow, indicatingthe directionwhichgives the recorded sense of asymmetry.

Fold Axial Traces - Intersectionof foldaxial surfacewith land surface.

—..--

, Ant iform,

, __X—, Synform

:ost of ths rocbs ocourrs sn the area have bcon

doscrlbcd feiriv adecoad-e'r_ aeny authors in the pact.

e main netrograohic observogion aed- this susaer is the

foct that petrogra hic distinctions can be aode id

easi1:7in rOcks yin tO the north of Tokken which have

been lergeT7 ,isr oded until recentl gronoed

together as kice schists of the Gu-te

It has boon very easm to aao a band of

11 ouartr rich, blotite flecked, Laainated aica schist

ch . ou both sides of the

Svorkko Antifora. his bend thins out weob.Yerds, the

sputhern outercp Jisa- earin furoher to the east then

the northern one. Hence the facial Ltnit of this litholo

trends very s ighti dduely to the f2 foLd exial

direction. ?his likit 7 rooresent a true facial

or it nav reoresent the hinge of an f, syncLinal napre,

a noso*-12-surk.'sortntneseds'enbinf,structures.

The f ,gy quaZ.tzschist occurs in an undifferenti mbe

sequence of nredoainantly black or grog.quar

schists. Ted ing is frequentiv soen, end tho sch sts

apo.earto be lithologically s ailar to the chlor te s

but with a aach less basic CO=Ositt=.

In the horth and gsostof the erea kacoed the sch nts

are kodchrioreacidlc, and ere of garnet grade. FrecuentLy,

lenses of ouertz-feldspar segregetion are seen interdalated

within the schists, which are structurally the lowest,

and probably also ttratigraphically the oldest rocks

9

in the area. However, the metamorphic grade boundaries

probably cut auite obliquely across the f1 structures,

and are folded by the f2 structures, so it would

be wrong to make any inferences of age from metamorphic

grade.

GEOCHEMISTRY

The investigationof chemical variationswithin'

lava pillows and between lava flows is not yet complete.

Thin sections have been made of all the 40 or so rocks

which are being analysed, and a precursory examination

of these has suggested that a number of volnic

horizons exist within the area which are truly intermed-

iate in composition (keratophyres).These rocks have

a sub-spherulitictexture, and in hand specimen have

an appearancewhich is impossibleto distinguishfrom

thoroughlybasiclavas!

•

30 c m.

-

ty

15 cm.

(d)

30 cm.

NOR TH

(d)

10cm.

Seco::dfold in Llicisdhist North of Dragset.

Refolded first fold in chlnrite schist N. of Svorkmo

Anfiform.

d):3edding/cletwageand refracted cleavage relations

in chlorite schist north fro Løkken.

3efoldod first fold in mica

Note folded first lineation

lineation C.

schist north of I-Akken.

B folded around second

Ah outdihe of the geoLo.gicalstructure of the area

s ho paher submittod to dn 1967. d'his

ihter-ro.,AA, uoe general structural geomet and

history of the area na5 been further corroborated by

v:hat have fo d in the nast few wees.

• _

7he f9 adifor compleme tary to the Aøkkeh

syhform, perhass •est oonvonte1v caLled the Svorkmo

ifhhm, sdocc its htre trace hasses through the

vddLage of Svorn ocen mapped from Dragset edne

to the 'vorksdOen area bg onn atthev:sand myself.

?he fold profile is usually tight to lsoclihal, wita the

axial surface either verdical or ovorturned totTardthe

iorth. ?r- r cL t at tne Tahk.a -5ridSvolsmo fold axdal

surfaces are 5L'ghtlg incidned dh ophosime ddrectdens

thicMness Yardatleas tHee

edlhotarv sequence. The form of these

,,kEt17suggestod dh the aceomhanytas hrofdLo

soctto'h.Tess racid hickhess ahd facles chahgcs ta-teolaeo

alohg the fo axdal directdon, though there ahnyearsto

ec a genceal thinning and fold tigateh g westward.

-Sac'bof oxoosure in the area north frws firagsetIdne

s asia dt imhos-ibLe in a short time to delineato the

:or foLd form dth eortaihty, but dt appears that

the axiaL traces of the Svorkmo Antiform and the

comhiemehtnry synform to the north aphroach each othcr

(40nikricoaCh

tho sectoea north fraM RøryandEt it is

not boon possible to fina either the Evorkmo Antiform

or Lekken Synform. In all exeosures tho f,

istosity rly vertical and thore is often a

strong f, crenulation eleavage at a small angle to_

the f sehistosity. It is erobabde that the lekken Synform

sti" exists in tnis area but that it is isoclinal.

The Evorkmo Azt orm may or may not exist.

Ene of the eureoses in extendin t maeni west

te Rervh Gt was tG determine the ferm of the euartz

kerato hyras in that area. These rocks sim1y occur in

tee form of humber of vormieal lenses within tne

sc:_k sit1. Thoyare largely cut offby a fault in

the east. The rocks are extremev massive, euattz rich

ana fine orsined. They weathGr into prominent riais_=;es

seearatei by boggy valleys containing chlorite schists

which aeGear to be basic igneous rocks, The adid rocks

may not have Soen thinned greatly in the deformatisz of

the area, siflcethey are even now very thick comeared

with their latoral extenf.

Korth from the Svorkmo Antiferm, tho comelementary

synform can be actected. This structure is markealy

overtosned toward the north, par;icular flthe -;:est.

Phe aorthern _aaak of the synform is very extensive,

"e aia ehstes nerth of Dragset the asymmetric

in the strite of the f, schistosity arsund the

hiage of the synform is very cGearly seen. It is erobable

12

that somewhereon this flank the core of the f1

synclinalnappe outcrops, so that further north still

one begins to pass down the stratigraphicsequence into

progressivelyolder rocks.

The principle of asymmetry of minor folds indic-

ating the form of major folds does not appear to hold

well in the case of the Svorkmo Antiform. Incongruous

minor folds have b een found on the flanks of the major

f2 folds, often coupled with intense crenulation

cleavage, at a number of localities. It may be possible

to fit these in with a continuous strain distribution

(i.e. continuousf2 cleavage pattern)when the effects

of relative developmentof cleavage and bedding in the

formation of f2 folds is considered.This will be

more fully discussed in John Matthewfl report, with

particular reference to the remarkabledevelopmentof

this phenomenonin the Svorka River section.

0;tune;DA22",)?..1002.1jot2.IOLZC)21•

..ZOJ

e2.-tu-JeT0;g3e:oftoTsug

20=egso?ru=...oguueU000.1p2.22OT-,224SC2.2.2.S-pUS

12uT=3Jc'cCcTL:ccc=T.T0IY0JcCicc.

dcJontneSOTT,.dr.o.LcTier49og;u0.7-..nit0n2;s

074J1TUTJ00PJO2.-2:.:U.I9T:11CJ?,90Gq2,1:-.10Jj2

20.100tr0"RUE'GUIGUA209223=.11flG.281:

CLTDJOCOTT„:P4E072.

=ITT2":22'',TSOTS;209

U=4.0ocee:zo0A:p2o:2/T_cy2eg?,.Y.,22

:72:3TL22,:f,72:2001=fl9COr"fl..71J3JUT20009AUg

El9a2I.00T00-0A,1:1PU:eTuL^eunuTo:

.togpejJO00222u0.O95000099TIJC..tL014

TIMUCL:OJJ:=70•14I014-7.01::0T.c(52.03 022,UTeEnui

/.10117joO7POLIIjeogesez.324UTUXO

0,1,240n.T2c2Tcen?,•=;Jog;To..,.T2.22-;22,TO

ng=doTGA:n011Get'2014e0epe1201T=3e.zor.:2

ce.J.nnrcu_ns222egn

g2,71.720,(:; 7jeJj'inne:Leg20.12tGT1I:02.no2

2.1.3120022„OnAT2rge.2

'uoTTeee,OTJOO011uer0^.20T-E2;GI.49UT:OUX9I=0:1472

0141peuTo;ee01JIOJIlD90100.7.022.70.t0220egi

jo220e14TiUr-dUT.09,,T100/};G2T5JuT.Inr,e)go.-c-u

snuTod020e:JuipJu:h.)..TSTUOTOSIIOSID31:00

6.1.0=0Mjoo;.sc:oc.Jano.gs

UTAC_JO00.1012001.10euop7000:102

14

display the bedding/cleavageand younging relationships

shown on the profile section to a remarkable extent.

This is the prime justificationfor the nappe structure

indicated on the sectinn. Unfortunately,theaxial

surface trace of this nappe appears to be entirely

above erosion level. The axial direction of the f1 and

f2 folds is apnroximatelyhorizontal, despite plunge

culminationsand depressions,so parts of the nappe

structureabove the erosion level at Løie[endo not appear

to be brought lower down either to the east or to the west.

The bedding cleavage relations observed in the chlorite

schist are'consistentas far notth as th southern outcrop

of the flaggy quartz schist, and north from the northern

outcrop of the flaggyquartz schist. Inconsistent

bedding/cleavagerelations are observedwithin the

core of the Svorkmo Antiform. This suggests that the

synclinalnappe core outcrops in the core of the Svorkmo

Antiform. The nappe core is indicated on the profile section,

though the axial surfnce trace cannot be delineatedwit h

the confidenceimplied! The suggestionis made as a

working hypothesis.

15

FAULTING AND JOINTING

A fault zone of considerableim-portancehas been

observed running north-south through Ringavatnet.

This fault runs for about 5 km. in the mapped area,

and appears to end just west of Dragset Mine, amid a

group of splay faults.

This fault is undoubteåly the southern contin-

uation of the fault which divides the Gangås Group

of Peacey (1964) from older rocks to the west.

The fault makes a marked topographicfeature between

Ringavatnet and Gangåsvann. Its importancelies in the

fact that it separates the CambroSilurian rocks of

the TrondheimRegion in the east from the Basal Gneiss

and Sparagmitein the west, hence a large downthrow

to the east may be inferred. This is consistentwith

theway inwhiohboundariesaredisplaoedin this

area. Peacey has suggested that a movement of at least

6 km. has taken place in the central part of this

fault% zone.

No new measurementsof joint surfaces have been

made this stmmer, since it is consideredthat the

analysis of joints presented on a previous occasion

is an adequate description of the joint pattern in

the area.

sotro y ef a nn000r of ine 015 irl:A5

elf nt thrce doendltdde

- tcroo

.0 0 nor

OX-Oe• vnrissie stat000

, s aroxiaattras to trtaxtal eliJnnotjs

nTorecnoeon, and the ofaxid terLed te and oinisouo

ons and Z resnocti cLy, v:oreme—drod.

and b=d:/:: ,ed, and

o ottee aeaiast

snon deforo.

the feeld ef " ntton. oblnbe

rons the eddlpsodde

fic "constricted", orolnt- eldisolde.

0:1:,-.00:t0, L.,:i‘i hiCh

OlOti=" :riCti--:-.0:..11

f'oro dav.s -±,05 ett

devns nnere trons;otretchs

co- on nt of toonl strnin .1nr ofonntdon,

or tnnt - nqnsrod

no dnnse nndsotrony otno „ dno to Ila

onodsontdond r eOneet

tc :ocal The roch fnoios ernrintlone

endicnto nredwolnnntly enet- t tonoserapnicfentaron

cl condd c incordorated itto t :il 0 _ckS

sh2.,T3anesotrony. dt is adso noseibde tha

rofdrocta co:deln:.tSonof both e

ler ddocuerion of tne :sonernlfentnron of

17

lava deformationand their possible use as strain indicators

is required, and this will be undertaken by Mr. Matthews.

Deformed conglomeratefragments are also promising

for use as strain indicators,but their use will probably

rere tedious preparation of material. The use of

Flinn diagrams, and the general problems of using

deformed conglomeratefragments as strain indicators

are fully discussedby J.G.Ramsay (pp.185,Folding

and fracturingof Rocks, Pub. McGraw-Hill,1967)

•

•

03=,0 Of ohe close na-ni_ of the

is CilEhICU:tto derive

unorui infornation from a study of linsation deform.ation

in this srea. Uonzever,information is comirs,to light

sugsests that more attent'on should be taid

to such fsturts. It has hcark:,;:oundthat in the hinte

50:1j5 folds, the ±h idaeations cross at

dos to Hhe f„)..axialdireetion. his

tnd, a stro strair.cwconent :

svcrtrint buchling, esneciald in the case of

"olds in 4ha more sehistosc rocks.

Therc are two main aphroaches to the analvsis of

doformed lineations :

?he diechnieueof Construction of lineation Isog —d

:ans.

This technique •casrecentdy discovered by Cr.

C. Dlflott, a conv of v:hosetaner is

thiS renort. Che basie nrenciseis that lineation

isogonic surfaces are parallel to oce udn isogonac

SurfaCcs of J.dbY folds. Lhds technicue rca::ultimateiy

nrove LÀ5UL for the Cetection of eardy folds, but oni

.mhon a latro sumbor of readings have been callected,

more so than via ave collected to date.

r2he?echnieue of Stereographically IslottingLineati n

Vector Loci.

2his teenaisue can be used to determine the mechanics

of later folds, and is fully described by Ramsay (1967,

19

pp. 461 and onwards). It is the applicationof this

techniquewhich has suggesteda flatteningcomponent

in the hinge of the f2 Svorkmo Antiform. The results

will be discussed by Mr. Matthews.

•

•

20

beliove thnt in the future it bscome

necsspyry to aaalyso geo1ogica1 orientation data

in a more systomatic 1n particular, objective

statisticbl met ods must be brought to bear, and this

is prohaby of sarticular importance in the minirg industry.

Such Probably require the application

of electronic cem-uting techniques ih viev:of the

_args amount of data involved. prersqui ite to this

is the systwentic storage of data on coding sheots

Ps ,t is acduirso,to facilitate retrieval for

subsecuent processing.

Suring the Past year some considerat_on has been

given to tho Problem of statistical analysis of orientatioh

dnta. A test of the possib(lities of this typs of

analysis vgesgad- oh the data colleDted . Shapi=

last sumher in the area .set o' Sravset inc. dhe

data --P anelyssa using the 1mperial Oollege

7094-1401 computer system. ?he method employed

v:asdescribed in a thesis submitted by Dr.T.V.Ioudon

to the United States Office of Saval Rosearch in 1964.

dho theory 0f the eethod is outlined in an extract

fr •m,this thesis subpiittedwith this report. dhe

prOTra involves the fairlv stur tforward

translation of the mathemntics into SOS(22AS10/.

The cpm-uter output ( except for most of the lists

of direction cosines transformed to leeferto the

71

crinoi sx_s) is cnclosed for reference surseses

with this ranort.

lhe fello. ng discussion nresussoses that the ronder

be familiar with the analysis of houdon.

ways in which statistical orientation data

analysis c-n aid in objective fold descristion are

as follows

- give a vzsual slot of soles zo the folded

surfac s. 2ho existing Loudon srogram Zn fact alots

the data on an ccual angle projectian after counting

aaints on tne esantorial slane, a riethodwhich leavos she

arojectian sanutable for co_an_t3ag.A1so,the counting

interv• is rather small. A subroutinc which slots the

data on an ecual area arojectdan after counting on the

surface of the sshere with a i sercent aran caunting

cone han now baen written, and this is nvailable for

future wore. •raistethod of counting no:es ent-Lrely

obviates the inaccuracies of the conventional oounting

techniaue which were pointed out by Strand in horsic

Geol. Tidsskr.,1945.

:otc=ination of the Fold Axial Surfaces.

Lha thefold aKial surface cdn defined by two of

princicai xas of zhe distribition of the fold surface

calas, crevliLd t at the re_wdata ars transfaraed

accordng to the relntive areas and wzounts of exsosure

on cach fold limb. Tioudon'sanalysis does take

account of field condZtions and it assumes that the raw

data aro obtained uniformly distributed over each

22

fold limb. This is generally not the case, since although

the 3 axis of the distributionis usually a good measur e

of the fold axis, the 2 and 3 or 1 and 3 axes will

bear no relation to the axial surface unless the data i s

uniformly distributedover the fold limb areas, or

unless it is transformedto be so. Fortuitously,the

Dragset data fulfills the desired conditiond,and the

analyticallydeterminedprincipal axes agree well with

the intuitivelyinferred principal axes.

As Loudon has suggested,the variance of the distr-

ibution about the three principal axes is a good

measure of thefightilessof folding about each.axis.

3) Determinationof Fold Asymmetry.

Loudon's treatment of fold asymmetry does not

take account of the fact that asymmetrymust be expressed

by at least two independentparameters

p = 11 / 12

This describes the asymmetry of a single

folded surface.

q = sin øl / sin ø2 = t1 / t2

This describes the asymmetryarising

from differences in layer thicknesses.

23

The position of the axial surface is defined by

the hinge lines of adjacent folded surfaces, and hence

the analysis into principal axcs should involve this

latter symmetryparameter.

A fold only possesses orthorhombiesymmetry if

both of the following conditions are simultaneously

satisfied

11 sin ø1= 1 , and

12 t2

4) Determinationof Curvature.

A fold can be defined as the family of curved

surfaces between adjacent limb inflexion surfaces.

ti= 1

tivIcLEmori SQRFACC

eir Fot-2) sinzgAcE

FOL-3

)NFI-' ÀlO.J SOI2F/REJ: P

oNE

"VoLwme

..."'..--

.......- / /.../- / /

/ ///

The curvature of each fold limb may be different,'

and hence each limb should be analysed separately.

The variance about the vector mean of all the data

collectedbetween each inflexion surface trace and

.hinge trace on the mapwill give a measure of the

curvature of each limb.

24

Determinationof InterlimbAngle.

For orientationanalysis thislis most conveniently

defined as the angle between lines joining inflexion

points to each hinge point on each folded layer.

This measure is given by the angle between the

vector means of each fold limb, and is in my opinion

a better descriptionof interlimb angle than the con-

ventionally adopted definition of the angle between

the tangents to the limbs at each inflexionpoint.

Analysis of Cylindricity.

This is treated as a prtIblemin the analysis

of bivarianceby D. Cruden, a copy of whose paper

is includedwith this report. The treatment is

probably unnecessarilytedious, and for practical

purposes it may be more convenientto adopt the

traditionalmethod of"analysis in subareas",wherein

folds can be considerednearly cylindricalover a

selected axial length. The orientationof the great

cirele which best fits the data can then be determined

by the least squares method. The variance about the

3 axis is, as suggested by Loudon, probably the most

convenientmeasure of the cylindricityof folds.

25

A prerequisiteto the statisticalanalysis of

orientntiondata is the organisationof the data into

blocks distributedaccording to 1) fold limbs, and

2) approximatelycylindricallyfolded areas along the

fold axial direction.This is most convenientlydone

by drawing hinge traces and inflexiontraces on the

map, and by using lineation plunges, to pick out areas

of approximatelyequal plunge, within, say, ten degrees:-

1-1vPoTHETICAL S'XI,MPLE

-4--il

Ral-26 i.

HitLvniCt‘

=

. )/1111" 9=05.-k

'TA LN.

N1........ %

æ ."----. I ;11-imil P ,93 /‘ l' / ), AT0' aLoci( Q,1 I

al H

r•kfrda, 4 iltal '''=,

4. Lwv. 11:7-zo° M.1,(44C

puiNG.E ov E.e. la

H T-- HINC.6 7-/tACE- iNFLEXIOni 7-R4CE

26

Now, taking a profile section across an hypothetical

folded layer :-

L . et/\ Surr"ce

a, Rt ot2 OSe r e p re4 "1; na

4) &o1-Aeotik.c.oeeAreas kiween

hin,e ik•Nce And illiCier;on-

Lraces. J442.e,therp7nt-s kne been ols:k1kr4fily

ÇQL-1 AAML raiNe c-Aeset E.sca c e

In order that the 1 and 3 axes define the fold

axial plane :

Number of readings on limb 1,= r1 ' is proportional

to 11 ' sin1

A similar relation exists for limb 2.

Hence the .ratioof readings on each limb :

r1 i l • sin øl 11 • t,= s = p q

r2 12 . sin Ø2

Now ,

a1 sin øl 11 cos 0(and

a2 sin Ø2 cos

by inspection.

cos «Hence, p • q = (1)

a2 . cos /3

27

Thus fole'asg 0,rg can be expresso oj two

ddmonsionloss narameters which nre easdly comuuted.

Tt ds ---o tant to uote that tho ratdo of layer

thcknesses is ecual to the ratdo of ddusboutcron areas,

a corolidrY of the fact thnt the orientatden of folded

layers ds entdrelj a functlon of the tkickness of those

layers. The wide outcrop of the southern ldmb of the

TIkken Synform, due to the thickening of the Støren

Group metavolcanics southward, is a case in point.

cuantitdes cosp< and cos/3 can be detsrminod

ddrectlY frem the vector mean of all the assombled data

for each dimb, and the ratdo a, / a ds ddrectl-,

deterudned from the measurod map areas between each dd u

and inflexion trace. The anipulatdons of the data

to satisfy relation (1) are then most conveniently

carried cut in the computer as part of the program.

The results of this type of analysis are a number

of vector cuantities duscrdbi-- the orientntdon of

the fold in spacs and a humber of dimensdoniess

uarameters descrdbing physdcal attrdbutos 3f tho fold

such as asy--etry, tdT:htness,curvature of ldbbs,

cyl indri otc. ?hese parameters ais.t usefully

be dTs •la d Tra:)hict_17to shocrthe way in which

vary over the whole region. Such a treatment might

usefully pdck out systematic vardatdons in fold

Ye-met-v •r-dch--c reflectdehs of ldthslogv and thdckness,

i.e. facial variations, which might otherwise not be

apoarent.

28

•

I shall be prepared to undertake sch a computer

analysis of this type, of orientati-ndata from the lAkken

Area, should it be desired at any time in the future,

The data should be organised into limb "blocks",

as illustratedearlier, and listed in columns headed,

"azimuth"and "amount of dip" ( i.e. data must be in

the form of dip and dip direction,NOT dip and strike).

A map should be made showing the way the area has been

split up into subareas defined by inflexionand hinge

traces in one direction and zones of approximately

constant plunge in the other.

29

CORRELATIONWITH NEIGHBOURINGAREAS

Time has not permitted an attempt to make

a definite correlationof structureswith the

areas to the east. One thing has become apparent,

however, and that is that the fold phase which

Carter describedas f1 is thecquivalentof what

we have called f2. Hence the swing in the strike

ot the rocks around Hølonda must be attributedto

some event later than our f2.